Synthesis,in vitro antibacterial and antifungal evaluation of novel 1,3,4-oxadiazole thioether derivatives bearing the 6-fluoroquinazolinylpiperidinyl moiety

A series of structurally novel 1,3,4-oxadiazole thioether derivatives (6a-6z) containing a 6-fluoroquinazolinylpiperidinyl moiety were designed and synthesized using pharmacophore hybrid approach, and their structures were fully characterized by ¹H NMR, ¹³C NMR and HRMS spectra. Among them, the structure of compound 6d was further corroborated via single-crystal X-ray diffraction analysis. In vitro antibacterial bioassays showed that compounds 6a, 6g, 6u and 6v possessed EC₅₀ values of 30.4, 30.6, 27.5 and 26.0 μg/mL against phytopathogenic bacterium Xanthomonas oryzae pv. oryzae, respectively, which were significantly superior to that of commercially-available bactericide Bismerthiazol (85.1 μg/mL). Moreover, in vitro antifungal bioassays indicated that seven compounds demonstrated broad-spectrum fungicidal acitivties against six types of phytopathogenic fungi at 50 μg/mL. The present work showed the potential of 1,3,4-oxadiazole thioether derivatives carrying a 6-fluoroquinazolinylpiperidinyl moiety as effective antimicrobial agents for crop protection, deserving further investigations in the future.